Overtemperature protection system for a solar water heating system

ABSTRACT

The invention provides a solar hot water heating system including one or more solar energy absorbers ( 102 ) having at least a first fluid circulation path wherein, an over temperature path ( 119 ) is provided, the over temperature path including a pressure vessel ( 120 ) which is normally closed to atmosphere, the over temperature path being connected to the first fluid circulation path ( 108 ) so that, in the event that fluid in the solar energy absorber vaporizes, the fluid is forced out of the solar energy absorber and into the pressure vessel. The present invention also provides a temperature sensitive valve leaving a flow path and a valve member operated by a thermal element having thermal expansion characteristic the valve including a support member against which the thermal element expands to force the valve element to close the flow path.

FIELD OF THE INVENTION

This invention relates to an arrangement for dealing with the effects of overheating in solar water heating systems.

BACKGROUND OF THE INVENTION

Solar water heating systems include a solar collector which acts to convert solar radiation to heat energy to heat water. Usually this involves a solar panel having a heat transfer fluid which absorbs the solar energy, the heat from the heat transfer fluid being transferred to the water via a heat exchanger. The heat transfer fluid may be water with additives. Solar energy is an unregulated source of input heat energy. Thus, there is a possibility that the heat transfer fluid will boil if the rate of energy input from the solar energy exceeds the rate of heat removal from the heat transfer fluid. Boiling of the heat transfer fluid may damage the solar water heating system due to excessive pressure.

Any reference herein to known prior art does not, unless the contrary indication appears, constitute an admission that such prior art is commonly known by those skilled in the art to which the invention relates, at the priority date of this application.

SUMMARY OF THE INVENTION

The present invention provides a solar hot water heating system including one or more solar energy absorbers having at least a first fluid circulation path wherein, an overtemperature path is provided, the overtemperature path including a pressure vessel which is normally closed to atmosphere, the overtemperature path being connected to the first fluid circulation path so that, in the event that fluid in the solar energy absorber vaporizes, the fluid is forced out of the solar energy absorber and into the pressure vessel.

The present invention also provides a solar hot water heating system including one or more solar energy absorbers having a heat transfer fluid circulation path, therethrough, the heat transfer fluid circulation path including a heat exchanger, wherein, an overtemperature path is provided, the overtemperature path including a pressure vessel which is normally closed to atmosphere, the overtemperature path being connected to the heat transfer fluid circulation path so that, when heat transfer fluid in the solar energy absorber vaporizes, the, heat transfer fluid is forced out of the solar energy absorber and into the pressure vessel.

The heat transfer fluid circulation path can include a valve arranged to facilitate the evacuation of heat transfer fluid from the solar energy absorber under the pressure from evaporated heat transfer fluid in the solar collector.

The valve can be a one way valve.

The valve can be a pressure actuated valve.

The valve can be a temperature actuated valve.

The valve can be a controllable valve.

The heat transfer fluid entering the pressure vessel can increase the pressure in the pressure vessel, so that, when the temperature of the heat transfer fluid vapour in the solar collector falls below the vaporization temperature, the pressure in the pressure vessel forces the heat transfer fluid back into the heat transfer fluid circulation path and the solar energy collector is replenished with heat transfer fluid.

The overtemperature path can include a pressure relief valve.

The pressure vessel can have a substantially tubular shape.

The pressure vessel can be inclined at an angle to the horizontal.

The pressure vessel can include a riser.

The pressure vessel tube can be formed from a pipe suitable for use as a flue in a centrally flued hot water tank.

The present invention also provides a temperature sensitive valve having a flow path and a valve member operated by a thermal element having thermal expansion characteristic, the valve including a support member against which the thermal element expands to force the valve element to close the flow path.

The valve can include a hollow body containing wax and a piston.

The piston is spring biased to tend to compress the wax.

BRIEF DESCRIPTION OF THE DRAWINGS

An embodiment or embodiments of the present invention will now be described, by way of example only, with reference to the accompanying drawings, in which:

FIG. 1 is a schematic drawing of a solar hot water heating system according to an embodiment of the invention;

FIG. 2 shows a solar collector and heat exchanger arrangement including a thermal overflow vessel according to an embodiment of the invention;

FIG. 3 shows a detailed view of the connections of the heat transfer fluid and water lines to the heat exchanger;

FIG. 4 shows an alternative arrangement of the overflow tank;

FIG. 5 shows an alternative configuration for the overflow tank;

FIG. 6 shows the overflow tank connected to the inlet side of the solar panel;

FIG. 7 shows a temperature sensitive valve suitable for use with the present invention;

FIG. 8 is an exploded view of the valve of FIG. 7; and

FIG. 9 is a further view of the valve of FIG. 7, showing a bias spring.

DETAILED DESCRIPTION OF THE EMBODIMENT OR EMBODIMENTS

The invention is applicable to systems in which potable water is heated directly in the solar panels, and to systems in which a heat transfer fluid is heated in the solar panels and then passed through a heat exchanger where the heat is transferred to the potable water. Embodiments of the invention will be described with reference to a heat transfer fluid system.

FIG. 1 shows a solar water heating system including a solar collector 102 connected to a heat exchanger 116 by pipes 108, 110, which elements form a heat transfer fluid circuit. In this embodiment, header tanks 128 and 130 are used to collect the flow of heat transfer fluid from an array of channels 132. In the field, the major plane of the solar collectors is usually oriented at an angle to the horizontal resulting in an upper end defined by upper header 128 and a lower end defined by lower header 130.

Heat exchanger 116 may consist of a water tank surrounded by a heat transfer fluid jacket. However, other heat exchanger arrangements can be used. Heat exchanger 116 has cool water inlet 114 and hot water outlet 112.

In a thermosyphoning system where the height (gravitational) differential and the thermal differential are sufficient to overcome flow resistance and produce a required flow rate, the heat transfer fluid is heated in the solar panel channels 132 and rises under convection to the header 128, passes through pipe 110 to heat exchanger 116 and returns to lower header 130 via pipe 108. A flow control device 122 controls the direction of flow between the heat exchanger 116 and the solar panel 102. The flow control device can be, for example a one-way valve or a controllable valve.

The expansion vessel 120 can be connected to the heat transfer circuit at any convenient point. It can be connected to the outlet side of the solar panels 102 as shown in FIG. 1 or to the inlet side of the solar panels as shown in FIG. 6.

Where the gravitational and thermal differentials are not sufficient to meet the heating performance requirements by thermosyphoning, the heat transfer fluid circuit can be pump driven.

The thermal overflow vessel 120 is connected to the heat transfer fluid circuit. The overflow vessel 120 is normally sealed to atmosphere, but can be provided with a pressure relief valve to relieve pressure above a predetermined value.

The overflow vessel can be connected to the heat transfer fluid circuit in a manner which facilitates the evacuation of heat transfer fluid from the solar collector 102 when the heat transfer fluid reaches its boiling point. This can be achieved by preventing “reverse” flow of heat transfer fluid into the top of the heat exchanger 128 via pipe 110, for example by a valve 122, which may be a one way valve, a pressure operated shut-off valve, a temperature operated shut-off valve, or a controllable valve which prevents the flow of heat transfer fluid into the top of the solar panel 102 via pipe 110 when the heat transfer fluid boils.

As a consequence, when the heat transfer fluid begins to boil, the vapour will rise to the top of the solar panel 102 and also generate a significant increase in pressure. That part of the heat transfer fluid which is still in liquid form is forced out of the solar collector 102 through pipe 108 by the increased pressure. Because the overflow vessel 120 contains compressible gas, and is connected to the heat transfer fluid circuit, the heat transfer fluid forced out of the solar panel is forced into the overflow vessel 120 via pipe 108, and, in this embodiment, through heat exchanger 116. As heat transfer fluid is forced into the overflow vessel, the gas in overflow vessel 120 is compressed and this increases the pressure in the overflow vessel until it is sufficient to prevent further heat transfer fluid being forced into the overflow vessel 120. The volume of the overflow vessel 120 is selected to permit the overflow vessel to contain substantially all the heat transfer fluid in the solar collector channels with sufficient volume for the gas in the overflow vessel to be compressed to a pressure to balance the vaporization pressure. Preferably, the overflow tank can also accommodate a volume of heat transfer fluid corresponding to the volume of the upper header tank 128.

The valve 122 blocks the heat transfer fluid from being forced through pipe 110 to the top header 128 of solar panel 102.

Only a small amount of heat transfer fluid needs to vaporize to cause substantially all the heat transfer fluid to be forced out of the solar panel. When all the liquid heat transfer fluid is forced out of the solar panel, the heat absorption by the heat transfer fluid in the solar panel is substantially reduced because only vapour is contained in the solar panel.

When the overtemperature conditions are removed, the compressed gas in the overflow tank forces the heat transfer fluid back into the solar panel.

In cases where the solar panel is located above the other components of the system, the valve 122 may be dispensed with as the heat transfer fluid vapour will rise to the top and fill the solar collector, forcing the heat transfer fluid from the solar collector and preventing its return until the vaporization condition dissipates.

The heat exchanger can be located above the solar collector panels and the overflow tank can be designed with sufficient capacity to contain the volume of heat transfer fluid in the heat exchanger and in the solar panels.

The overflow tank 120 is preferably arranged to ensure that the heat transfer fluid can be returned to the heat transfer fluid circuit to recharge the solar panel. This can be done by the use of a riser pipe (c.f. 406 in FIG. 4), or by tilting the overflow tank 120 at an angle θ so that the overflow tank feeder pipe 118 is at or near the lowest point of the overflow tank 120, as shown in FIGS. 1 & 2. This provides an elevated region into which the gas in the overflow tank 120 is compressed when the heat transfer fluid in the solar panel vaporizes. This arrangement helps to prevent the gas in the overflow tank 120 from entering the heat transfer fluid circuit until the heat transfer fluid has been emptied from the overflow tank. invention.

FIG. 2 shows the layout of a solar water heating system embodying the invention.

A pair of solar panels 102, 104 have their upper headers connected and feeding to the heat transfer fluid input of the heat exchanger 116 via pipe 110. The lower headers are also connected and linked to the heat transfer fluid outlet of the heat exchanger 116 via pipe 108. The solar panels 102, 104 are installed at an angle to the horizontal so that the upper headers are above the lower headers.

A heat exchanger (116 in FIG. 3) is contained in housing 106 and is located above the solar panels 102, 104. Pipe 110 connects the upper headers to the heat exchanger 116, and pipe 108 connects the lower headers to the heat exchanger.

An overflow tank 120 is connected to the heat transfer fluid path in the heat exchanger 116 by pipe 118. This tank is effectively sealed to atmosphere, but may include a pressure relief valve to relieve pressure above a predetermined value. The overflow tank 120 is oriented with its axis at an angle to the horizontal so that the pipe connects near the lowest point of the tank and the gas will be compressed to the upper region of the tank as described above.

As seen in FIG. 3, the heat exchanger 116 connexions include water inlet pipe 114, water outlet pipe 112, heat transfer fluid inlet pipe 110, heat transfer fluid overflow pipe 118, the connexion of the heat transfer fluid outlet pipe 108 not being shown in FIG. 3. The hot water outlet 112 includes a pressure relief valve 134. Pipe 118 connects to the underside of the overflow tank 120. As the tank 120 is tilted to the horizontal, the connexion point of pipe 118 is at or near the lowest point of tank 120.

FIG. 4 shows an alternative arrangement in which the axis of the overflow tank 402 is approximately horizontal and a riser 406 is added to the tank so that the gas enclosed in the tank 402 is forced up into the riser when the heat transfer fluid in the solar panel boils. The riser 406 is closed to atmosphere at 408. Tank 402 is closed at both ends, and pipe 110 enters tank 402 at its lower edge.

Other configurations of expansion tank are possible. For example, as shown in FIG. 5, the tank 502 may be a drum shape, with its axis vertical. The base 506 is an inverted cone shape to funnel the heat transfer fluid back to the pipe 508 connected to the apex of the inverted cone. The top 504 is dome shaped. In such alternative embodiments of the tank, the lower surface of the expansion tank is preferably arranged to provide gravity feed to facilitate draining of the heat transfer fluid back into the solar panel as the evaporated heat transfer fluid re-condenses.

In a further embodiment, the tank may be spherical, with the heat transfer fluid pipe connected to the lowest point of the sphere.

In FIG. 6, the overflow tank 120 is connected to the inlet header 130 of the solar panel 102 by pipe 108. The outlet of the heat exchanger 116 is connected to pipe 118 via pipe 119. Again, the one-way valve 122 ensures that the heat transfer fluid is directed to the overflow vessel 116 when overheating occurs.

FIG. 7 shows a valve 700 which can be used to block the return flow into the solar panels when the temperature of the heat transfer fluid exceeds a predetermined limit.

The valve 700 includes a housing 720 which has a through bore 724 which is enlarged to form a chamber 726. The valve actuator is a thermal element 702, which is an elongate cylinder containing wax. The wax can be chosen to have a phase change at a selected temperature, such as, for example, 95° C. The wax expands rapidly at this transition temperature.

The cylinder 702 is closed at one end, and includes a piston at the other end, the shaft 714 of the piston projecting from the other end of the cylinder. The piston can be spring biased to tend to compress the wax. The cylinder 702 is attached to a valve disc 706 via a truncated conic section 707.

The piston shaft 704 projects into a blind bore 714 in a support member 710. This support member is provided with flow holes such as 712 to permit the heat transfer fluid to pass through the support member.

A closure member 722 closes the chamber 726 of the housing 720.

FIG. 8 is an exploded view 800 of the valve of FIG. 7. In FIG. 8, the numbers of the items correspond to the numbers of the items in FIG. 7, except that the prefix number 8 is used instead of the prefix number 7.

The housing 802 defines the chamber 826. The thermal element 802 is connected to the valve disc 806. A skirt 807 is attached to the disc 806 and provides flow apertures 808 so that heat transfer fluid can flow around the valve disc via these flow apertures. The chamber 726, 826 includes a portion of a larger diameter in than the valve disc 706, 806 in the region of the valve disc 706, 806 to permit the heat transfer fluid to flow around the edge of the valve disc 706, 806. A seal ring 818 can be provided around the periphery of valve disc 806. As seen in FIG. 9, the skirt 907 slides in the reduced section 930 of the chamber 926.

In FIG. 9, a restoring spring 950 is shown to return the valve disc to the open state when the wax cools.

The operation of the valve will be described with reference to FIGS. 7, 8, and 9. As the temperature of the heat transfer fluid increases, the wax expands in the cylinder 702, and the piston shaft 704 moves into the bore 714 until it reaches the end of the bore. Further expansion causes a reactive force between the piston shaft 704 and the end of the bore 714. This forces the valve disc 706 down to a reduced section of the chamber 730 so that the apertures 808, 908 are occluded by the walls of the reduced section of the chamber 830, 930, and the valve disc 706 closes off the flow through the valve 700. The seal 918 ensures effective fluid tight closure.

The reduced section 930 of the chamber permits over-travel of the disk 906 and skirt 907 to allow for the continued expansion of the wax after closure.

Where ever it is used, the word “comprising” is to be understood in its “open” sense, that is, in the sense of “including”, and thus not limited to its “closed” sense, that is the sense of “consisting only of”. A corresponding meaning is to be attributed to the corresponding words “comprise”, “comprised” and “comprises” where they appear.

It will be understood that the invention disclosed and defined herein extends to all alternative combinations of two or more of the individual features mentioned or evident from the text. All of these different combinations constitute various alternative aspects of the invention.

While particular embodiments of this invention have been described, it will be evident to those skilled in the art that the present invention may be embodied in other specific forms without departing from the essential characteristics thereof. The present embodiments and examples are therefore to be considered in all respects as illustrative and not restrictive, and all modifications which would be obvious to those skilled in the art are therefore intended to be embraced therein. 

1. A solar water heating system including one or more solar energy absorbers having at least a first fluid circulation path, wherein an overtemperature path is provided, the overtemperature path including a pressure vessel which is normally closed to atmosphere, the overtemperature path being connected to the first fluid circulation path so that, in the event that fluid in the solar energy absorber vaporizes, the fluid is forced out of the solar energy absorber and into the pressure vessel.
 2. A solar water heating system including one or more solar energy absorbers and a heat exchanger connected in a fluid circulation path, wherein: an overtemperature path is provided; the overtemperature path including a pressure vessel which is normally closed to atmosphere; the overtemperature path being connected to the fluid circulation path so that, when heat transfer fluid in the solar energy absorber vaporizes, the heat transfer fluid is forced out of the solar energy absorber and into the pressure vessel.
 3. A solar water heating system as claimed in claim 2, wherein the fluid circulation path includes a valve arranged to facilitate the evacuation of heat transfer fluid from the solar energy absorber under the pressure from evaporated heat transfer fluid in the solar collector.
 4. A solar water heating system as claimed in claim 3, wherein the valve can be one of: a one way valve; a pressure actuated valve; a temperature actuated valve; a controllable valve; or a combination thereof.
 5. A solar water heating system as claimed in claim 1, wherein the fluid entering the pressure vessel increases the pressure in the pressure vessel, so that, when the temperature of the fluid vapour in the solar collector falls below the vaporization temperature, the pressure in the pressure vessel forces the fluid back into the fluid circulation path and the solar energy collector is replenished with fluid.
 6. A solar water heating system as claimed in claim 1, wherein the overtemperature path include a pressure relief valve.
 7. A solar water heating system as claimed in claim 1, wherein the pressure vessel has a substantially tubular shape.
 8. A solar water heating system as claimed in claim 1, wherein the pressure vessel is inclined at an angle to the horizontal.
 9. A solar water heating system as claimed in claim 1, wherein the pressure vessel includes a riser.
 10. A solar water heating system as claimed in claim 10, wherein the pressure vessel tube is formed from a pipe suitable for use as a flue in a centrally flued hot water tank.
 11. A solar water heating system as claimed in claim 1, wherein the overtemperature path is connected at the to of the fluid circulation path.
 12. A solar water heating system as claimed in claim 3, wherein the fluid entering the pressure vessel increases the pressure in the pressure vessel, so that, when the temperature of the fluid vapor in the solar collector falls below the vaporization temperature, the pressure in the pressure vessel forces the fluid back into the fluid circulation path and the solar energy collector is replenished with fluid.
 13. A solar water heating system as claimed in claim 3, wherein the overtemperature path include a pressure relief valve.
 14. A solar water heating system as claimed in claim 3, wherein the pressure vessel has a substantially tubular shape.
 15. A solar water heating system as claimed in claim 3, wherein the pressure vessel is inclined at an angle to the horizontal.
 16. A solar water heating system as claimed in claim 3, wherein the pressure vessel includes a riser.
 17. A solar water heating system as claimed in claim 16, wherein the pressure vessel tube is formed from a pipe suitable for use as a flue in a centrally flued hot water tank.
 18. A solar water heating system as claimed in claim 3, wherein the overtemperature path is connected at the top of the fluid circulation path.
 19. A temperature sensitive valve having a flow path and a valve member operated by a thermal element having thermal expansion characteristic, the valve including a support member against which the thermal element expands to force the valve element to close the flow path.
 20. A temperature sensitive valve as claimed in claim 19, wherein the valve includes a hollow body containing wax and a piston.
 21. A temperature sensitive valve as claimed in claim 20, wherein the piston is spring biased to tend to compress the wax. 